A server computer (often just called server) is a computer system that has been designated for running a specific server application or applications. A server computer that is designated for generally only one server application is usually named for that application or purpose. For example, a server that runs Apache HTTP Server software, or Microsoft's IIS is typically designated as a web server, the computer running it is also simply called the web server. There can be web servers, database servers, application servers, such as: email servers or an Exchange Server, Share Point servers, Pre-press servers, Network Video Servers, Domain Controllers, and Network Storage or Backup Server. Server applications can be divided among application server computers over an extreme range, depending upon the workload. Under light loading, every server application can run concurrently on a single computer. Under heavy loading, multiple dedicated servers may be required for each application. Under medium loading, it is common to use one server computer (dedicated server) per server application, in order to limit the amount of damage caused by failure of any single server computer or security breach of any single server application. Any server computer can also be used as a workstation, but it is typically not, for support, maintenance, and risk management.

A server or server computer is also a designation for computer models intended for use running server applications, often under heavy workloads, unattended, for extended time. While any "workstation" computer can run server operating systems and server applications, a server computer usually has special features intended to make it more suitable, including more robust hardware and fail-safe technology. Distinctions often include faster processor and memory, more RAM, larger hard drives, higher reliability, redundant power supplies, redundant hard drives (RAID), compact size and shape, PC tower chassis with single or dual processors, or modular design (e.g., blade servers often used in server farms), rack or cabinet mounting, serial console redirection, etc. High capacity storage servers are sometimes called Terra Servers. Some servers are provided bare-bones, others built to order with numerous accessories, and others come preconfigured with the server OS and application software installed. Two very popular classes of servers are those based upon the Intel Xeon processor and the AMD Opteron processors

The name server or server appliance also applies to network-connected computer appliances or "appliance hardware" that provides specific services onto the network. Though the appliance is a server computer, loaded with a server operating system and a server application, the user need not configure any of it. It is a black box that does a specific job. The simplest servers are most often sold as appliances, for example switches, routers, gateways, print servers, net modems, hardware spam filters, and firewalls.